READ: Gallery — What Makes Humans Different?

It's hard to pinpoint exactly when and how collective learning first began. The following images, most of them created by contemporary artists, help us imagine how our early ancestors lived and shared ideas.

The making and using of tools, shown here in a reenactment, was thought for a long time to be a skill that distinguished humans from other species. But Jane Goodall's work studying chimpanzees and subsequent scientific observations have shown that other species are also capable of making and using simple tools.

Many scientists and scholars consider our use of symbolic language as the quality that really separates us humans from all other species. Ancient cave painting, perhaps the beginnings of written language, has shown up around the world and some examples date to more than 30,000 years ago – though the image here shows a much more recent site in Utah called "Newspaper Rock."

The ability to control and use fire is an important skill that helped enable humans to thrive by providing a heat source that was used for cooking and protection from the cold. Scientists do not know for sure when humans were first able to control fire but evidence suggests this occurred between 400,000 and 1 million years ago.

The mountain gorilla, shown here in this artist's impression, is a close relative to humans. There are distinct physical differences and similarities between humans and the "great apes" and primatologists like Dian Fossey also compared their social and behavioral characteristics.

In this artist's impression of Homo ergaster (also called Homo erectus), these ancestors of modern humans are shown competing with other species for a valuable food resource. Homo ergaster lived from about 1.9 million years ago until about 143,000 years ago.

Homo neanderthalensis are the closest of our extinct human relatives. In this artist's impression, Neanderthals are shown with tools and clothing. They are also known to have used fire and there is some evidence that they made symbolic objects. Neanderthals lived in Eurasia from about 200,000 years ago to about 28,000 years ago.

This is an artist's impression of Cro-Magnon Man, a term once used to describe some of the first modern humans who lived in Europe during the Paleolithic Era about 30,000 years ago. Now scientists consider this group to be similar enough anatomically to humans today that they don't even need a separate name designation.